The present invention is directed to a scrap submergence system of the type typically employed in molten metal processing. For example, it has application in the recycling of aluminum, but is not limited thereto. In the recycling of metals, it is necessary to melt scrap pieces for treatment and processing. A large portion of the scrap pieces are thin walled as a result of the mechanical shaping action from which they are formed, such as, shaving, boring and cold rolling. Melting thin walled scrap pieces is particularly difficult because (i) extended exposure to the hostile atmosphere in a traditional melting furnace results in extremely high oxidation loss and, (ii) rapid submergence in molten metal is severely hampered by the fact that thin walled scrap pieces float on molten metal.
In a typical melting operation, a melting furnace is provided with an enclosed hearth and a connected open melting bay or charge well. A pump or other molten metal flow inducing apparatus causes molten metal to flow from the hearth to the charge well. Metal scrap pieces are fed into the charge well. Pumps can be centrifical impeller driven versions or electromagnetic. This disclosure is compatible with either device but finds particular relevance to electromagnetic pumps which can be utilized in a dry hearth condition meaning a relatively low molten metal fill (e.g. <4 inches). Electromagnetic pumps work on the linear motor principal in which a conductor is magnetically repulsed by a magnetic field generated by the surrounding coil. Further details of the design, its principals and operation can be found in GB-B-2269889 the contents of which, particularly in relation to features of the electromagnetic pump principles and operation and system configuration, are incorporated herein by reference.
A variety of apparatus have been used in the melting bay (specifically in the charge well) to facilitate the submergence of the scrap metal below the surface of the molten metal bath. Three major types of systems exist. The first type includes mechanical systems constructed primarily of a rotor which creates a molten metal flow at the top surface. Examples of these devices are shown in U.S. Pat. Nos. 3,873,305; 3,997,336; 4,128,415; and 4,930,986. The second type of system uses a mechanical device to physically push the scrap below the melt surface (elephant feet/well-walkers). The third type of system relies on the shape of the chamber without rotation of a rotor to create a metal flow which submerges scrap pieces in the charge well. Particularly, the flow of molten metal into the charge well is manipulated in such a manner to achieve a vortex which draws chips from the top surface into the bath. These systems include, for example, U.S. Pat. Nos. 3,955,970; 3,984,234; 4,286,985; and 6,217,823, each of which is herein incorporated by reference. The present disclosure is directed to this third type of scrap submergence system.
FIG. 1 illustrates one prior art scrap submergence system of a type with which the present disclosure is associated. The apparatus includes a charge well 1 into which solid metal 3 is introduced so as to intimately contact it with molten metal 5. The charge well 1 has an internal profile which in combination with rapid molten metal flow causes a vortex in the molten metal surface which promotes the blending of the solid metal 3 into the molten metal 5. The rapid molten metal flow is generated by an electromagnetic pump unit 7. More particularly, molten metal 5 leaves the charge well 1 via outlet 9 and passes through conduit 11 into the furnace (not shown). Molten metal is drawn from the furnace by the pump unit 7 via conduit 12 and then introduced to the charge well 1 through 13 and inlet 15. The conduit 13 is aligned with the peripheral wall of charge well 1 in a substantially tangential manner to promote a vortex formation in the charge well 1. FIG. 2 provides a top plan view of a representative charge well.
Reference is made to FIG. 3 wherein a scrap melting device 100 is comprised of a block of refractory material 102 which can be constructed of a size suited to provide a relatively close tolerance mating with the dimensions of an existing charge well or could form a newly constructed charge well itself. Preferably, device 100 is constructed of a cured material such as an alumina-silica refractory or other castable refractory material known to those skilled in the art. Block 102 includes a chamber 116 having generally cylindrical side wall 118, a base wall 120, a ramp 121 disposed around an inner wall 122 forming a central cavity 123 leading to outlet 124 and outlet duct 125. Ramp 121 includes a leading edge adjacent the inlet 126 to the chamber 116. In practice, the device 100 has been found to provide superior scrap melting performance.
As stated previously, the present disclosure is not suited solely to recycling. Rather, at various stages during the melting, treatment, purification and distribution of molten metals it may also be desirable to introduce external materials in addition to scrap metal into the molten metal. These materials may be gases to extract undesired components from the molten metal, or powders to introduce desired components into the molten metal. The present disclosure also provides an apparatus and method for efficiently introducing such materials into molten metal. The apparatus and method advantageously provide greater contact between the material added and the molten metal as a whole.
The present disclosure further provides an apparatus and method having improved compatibility with the variety of molten metal furnace configurations that exist.